The present invention relates to a method for making multi-wall ceramic cores for casting multi-wall metal castings.
Most manufacturers of gas turbine engines are evaluating advanced multi-thin-walled turbine airfoils (i.e. turbine blade or vane) which include intricate air cooling channels to improve efficiency of airfoil internal cooling to permit greater engine thrust and provide satisfactory airfoil service life.
U.S. Pat. Nos. 5,295,530 and 5,545,003 describe advanced multi-walled, thin-walled turbine blade or vane designs which include intricate air cooling channels to this end.
In U.S. Pat. No. 5,295,530, a multi-wall core assembly is made by coating a first thin wall ceramic core with wax or plastic, a second similar ceramic core is positioned on the first coated ceramic core using temporary locating pins, holes are drilled through the ceramic cores, a locating rod is inserted into each drilled hole and then the second core then is coated with wax or plastic. This sequence is repeated as necessary to build up the multi-wall ceramic core assembly.
This core assembly procedure is quite complex, time consuming and costly as a result of use of use of the connecting rods, pins and the like and drilled holes in the cores to receive the rods as well as tooling requirements to assemble the core components with required dimensional accuracy.
An improved method is needed for making a multi-wall ceramic core for use in casting metals and alloys. An object of the invention is to satisfy this need.
The present invention provides, in an illustrative embodiment, a method making a multi-wall ceramic core for use in casting airfoils, such as turbine blades and vanes, wherein a fugitive pattern is formed having multiple thin pattern elements defining therebetween core wall-forming spaces, the pattern is placed in a core molding die cavity having a desired core configuration, a fluid ceramic material is introduced into the die cavity about the pattern and between the pattern elements to form a multi-wall ceramic core, and the core is removed from the die cavity. The fugitive pattern is selectively removed from the core to provide a multi-wall green core. The green core then is fired to develop core strength for casting in an investment casting shell mold. The pattern elements can be formed in three dimensional pattern configuration by injection molding, sterolithographic deposition of pattern material, and other techniques.
The multi-wall ceramic core so produced comprises a plurality of spaced apart thin core walls connected together by other integral regions of the molded core. The invention reduces core assembly costs and provides high dimensional accuracy and repeatability of core walls.